1. Field of the Invention
The present invention relates to a test terminal negation circuit in which a test signal from a test terminal is not received using a nonvolatile memory after a test is completed.
2. Description of the Related Art
Recently, an IC card on which a nonvolatile memory is mounted has been a focus of attention. Although a terminal of the IC card is standardized in ISO7816, there are various kinds of test terminals to facilitate a test. In a normal operation, since data is exchanged by authenticating the reader/writer and the like and encrypting the data, secret data is not leaked.
As a conventional technique, there is a method of outputting a test signal from a test terminal to a test object circuit by activating an output of a test mode signal generation circuit to turn on a switch circuit when the test terminal is used, and a circuit constitution in the method is shown in FIG. 3 (refer to Japanese Unexamined Patent Publication No. 2002-269523, for example). Referring to FIG. 3, each circuit comprises a test terminal 301, a switch circuit 302, a nonvolatile memory circuit 303 to be tested, and a test mode signal generation circuit 304. The switch circuit 302 is turned on when an output N3 of the test mode signal generation circuit 304 is activated, and then an output N1 of the test terminal 301 is transmitted to an output N2 of the switch circuit 302 to control the nonvolatile memory circuit 303. In addition, the switch circuit 302 is turned off when the output N3 of the test mode signal generation circuit 304 is inactivated, so that the output N1 of the test terminal 301 is not transmitted to the output N2 of the switch circuit 302. As a result, the nonvolatile memory circuit 303 cannot be controlled from the test terminal 301.
However, when a test mode is activated falsely by operating the test mode signal generation circuit for use other than the test, information in an IC card could be easily read out using the test terminal.
In addition, although Japanese Unexamined Patent Publication No. 2002-269523 discloses a method of erasing information stored in a nonvolatile memory in an IC card when it is detected that a test mode is activated falsely, it is necessary to provide an additional circuit to detect the false activation of the test mode in this method.